OBJECTIVE: To assess which ribosomal proteins are adjacent to RNA and how these relationships change with alterations in the structural and functional state of the E. coli ribosome. A rather large number of independent experimental approaches have been developed recently which when fully exploited will probably be sufficient to define the structural and functional roles of the various ribosomal proteins. Despite the fact that rRNA constitutes 2/3 of the mass of the ribosome our knowledge of its structural and functional roles is exceedingly limited as are the experimental approaches to these questions. Recently, U.V. induced covalent crosslinking between RNA and protein has been shown to be a powerful tool in analyzing the nature of the interaction between these two classes of macromolecules (Schimnel and coworkers, J. Mol. Biol. 84, 503, 1974 and J. Biol. Chem. 250, 4433 and 4440, 1975). I propose to apply this approach to the analysis of the disposition of RNA in the ribosome. APPROACH: 1. To prepare ribosomes radiolabeled in various specific ways in both the RNA and protein portions. 2. To irradiate these ribosomes with U.V. light so as to introduce covalent crosslinks between adjacent RNA and protein molecules. 3. To fractionate and analyze these adducts in various ways to determine which specific proteins and RNA's are proximate. 4. To determine how these neighbor relationships change as the ribosome moves through its functional cycle. 5. To determine which ribosomal proteins can be crosslinked (i.e., are adjacent to) tRNA and mRNA bound in various functional states and if various factors (e.g., IF-2, EF-G, EF-Tu) function on the ribosome in the vicinity of one or more RNA species.